FIG. 1 illustrates a typical top entry regulator, which has a valve body 10 defining a fluid flow path extending from an inlet 11 to an outlet 12 extending generally along the horizontal axis and valve trim opening 13 that extends laterally upwardly from the fluid flow path through a top side of the valve body. An actuator 14 is attached to the top side of the valve body over the valve trim opening 13 and configured to move a valve sleeve 15 up and down in the valve trim opening 13 so as to regulate the flow of fluid. A benefit of a top entry regulator such as this is that the regulator and the valve trim can be disassembled and removed from the valve body 10 without having to remove or uncouple the valve body from the pipes at the inlet 11 and the outlet 12. However, the circuitous route of the fluid flow path through the valve trim can reduce the flow efficiency of the valve.
FIG. 2 illustrates a typical axial flow regulator, which has an inlet flange 20, an inlet cover 21, an outlet cover 22, and an outlet flange 23, which are bolted together in-line with each other to form a fluid flow passage extending along a generally horizontal central axis extending from an inlet 24 in the inlet flange 20 to an outlet 25 in the outlet flange 23. A diaphragm 28 is clamped between the inlet cover 21 and the outlet cover 20 so as to form an actuator attached in-line along the horizontal central axis between the inlet flange 20 and the outlet flange 23. The actuator is configured to move a valve sleeve 26 that is axially aligned with, and moves back and forth along the horizontal central axis relative to a valve seat assembly 27. An advantage of such an axial flow regulator is that it typically has improved flow efficiency as compared with the top entry regulator because of the less circuitous route of the fluid through the valve trim. However, in order to access the valve seat assembly 27, for example for maintenance, it is typically necessary to remove the outlet flange 23 completely. This may require extensive labor and/or specialized tools to uncouple the actual flow regulator from one or both of the pipes connected to the inlet flange 20 and the outlet flange 23.